Detergent compositions in tablet form are known in the art It is understood that tabletted detergent compositions hold several advantages over granular detergent compositions. Examples of such advantages include ease of handling, transportation and storage. Tablets are therefore required to be of sufficient hardness such that they do not crumble or disintegrate on handling, transportation or storage.
Detergent tablets are traditionally prepared by the compression or compaction of granular detergent compositions. The most common method used by detergent manufacturers for increasing tablet hardness is to increase the compaction pressure of the machinery employed to tablet the detergent composition. EP-0,170,791 Henkel describes a process for making a tablet detergent composition comprising per compounds and tabletting aids. The detergent composition is compressed at a pressure of 5.times.10.sup.7 to 10.sup.8 Pa resulting in tablets having a breaking strength of between 50 and 120 N.
Other methods of controlling tablet hardness and dissolution have been discussed in the prior art. Detergent manufacturers have for example, introduced alterations in the detergent formulation, thereby changing the characteristics of the tablet. WO93/00419 Henkel describes increasing tablet hardness by providing a detergent composition comprising polymer. EP-0,466,484 and EP-0,522,766 Unilever describe increasing tablet hardness by providing a tabletted detergent composition comprising liquid binder and specific particle size ranges. Japanese patent application J06,207,199 A Kao describes a process for making a deterrent composition in tablet form wherein the process consists of mixing nonionic surfactant and an oil absorbing material, granulating the mixture to provide particles of specific size and density, then compacting the resulting particles to form a tablet. EP-0,579,659 Henkel, describes a process for preparing a detergent tablet wherein the alkaline detergent additives are agglomerated with builder, water and nonionic surfactant resulting in a tablet having a high break strength.
It has however, been found that ease of ejection of the tablet from the tablet press decreases with increasing compression/compaction pressure. Furthermore, the tabletting machinery at high compression/compaction pressure tends to damage the outermost surface of the tablet, as well as potentially damaging the machinery itself. Damage to the outermost surface of the tablet, such as scoring or scratching is unacceptable to the consumer. It is thus the object of the present invention to provide a detergent composition in tablet form that is not only sufficiently hard to meet handling, transportation and storage needs, but which can also be readily ejected from the tablet press without damage to the outermost surface.
It has surprisingly been found that by selectively spraying non-aqueous low viscosity liquid components of a detergent composition onto a specially selected low porosity fraction of the solid components of a detergent composition tablets that are more readily removed from a tablet press without damage are produced.